The present invention relates to a method and apparatus for conditioning a polishing pad. More particularly, the present invention relates to a method and apparatus for conditioning a polishing pad used in the chemical mechanical planarization of semiconductor wafers.
Semiconductor wafers are typically fabricated with multiple copies of a desired integrated circuit design that will later be separated and made into individual chips. A common technique for forming the circuitry on a semiconductor is photolithography. Part of the photolithography process requires that a special camera focus on the wafer to project an image of the circuit on the wafer. The ability of the camera to focus on the surface of the wafer is often adversely affected by inconsistencies or unevenness in the wafer surface. This sensitivity is accentuated with the current drive toward smaller, more highly integrated circuit designs. Semiconductor wafers are also commonly constructed in layers, where a portion of a circuit is created on a first level and conductive vias are made to connect up to the next level of the circuit. After each layer of the circuit is etched on the wafer, an oxide layer is put down allowing the vias to pass through but covering the rest of the previous circuit level. Each layer of the circuit can create or add unevenness to the wafer that is preferably smoothed out before generating the next circuit layer.
Chemical mechanical planarization (CMP) techniques are used to planarize the raw wafer and each layer of material added thereafter. Available CMP systems, commonly called wafer polishers, often use a rotating wafer holder that brings the wafer into contact with a polishing pad moving in the plane of the wafer surface to be planarized. A polishing fluid, such as a chemical polishing agent or slurry containing microabrasives, is applied to the polishing pad to polish the wafer. The wafer holder then presses the wafer against the rotating polishing pad and is rotated to polish and planarize the wafer.
With use, the polishing pads used on the wafer polishers become clogged with used slurry and debris from the polishing process. The accumulation of debris reduces the surface roughness and adversely affects polishing rate and uniformity. Polishing pads are typically conditioned to roughen the pad surface, provide microchannels for slurry transport, and remove debris or byproducts generated during the CMP process.
One method for conditioning a polishing pad uses a rotary disk embedded with diamond particles to roughen the surface of the polishing pad. Typically, the disk is brought against the polishing pad and rotated about an axis perpendicular to the polishing pad while the polishing pad is rotated. The diamond-coated disks produce predetermined microgrooves on the surface of the polishing pad. If the rotation is motorized, the motorization can be expensive and can experience mechanical failures.
Presently, polishing and conditioning are typically done on the same side of a rotating platen. On the rotating platen, there is polishing station and a conditioning station. Slurry is dispensed on the platen for polishing. The slurry that is exposed to air on the surface of the platen can eventually dry and crystallize. Some of the dried slurry can rotate around on the platen, making it back to the polishing station where it can then scratch the semiconductor wafer.
One known conditioning mechanism uses an arm having an end effector into which a conditioner pad fits. The arm moves across the polishing pad to condition it. There are problems with the known conditioning mechanisms that use arms. For one, the end effector used on these mechanisms rotates about a gimbal point that is internal to the end effector. This causes uneven wear on the pad in the end effector. Further, the known conditioning mechanisms with arms lack a reliable force feed back system. Previous strain gauges or load cells were mounted in such a way that dried slurry could build up and cause a friction force that would lead to inaccurate data.
The methods and apparatuses of the present invention address at least some of the problems of the prior art.
In one aspect of the invention, a conditioning mechanism in an apparatus for chemically-mechanically polishing semiconductor wafers comprises a drive mechanism and an arm. The arm has a first end portion, a mid portion, and a second end portion wherein the first end portion is connected with the drive mechanism, and an end effector is mounted to the second end portion. The end effector is adapted to receive a conditioning member for conditioning a polishing member. A strain gauge is preferably configured to monitor the force that the end effector, with the conditioning member therein, applies to the polishing member, preferably mounted to the mid portion of the arm.
In another aspect of the invention, an end effector in a conditioning mechanism in an apparatus for chemically-mechanically polishing semiconductor wafers is provided. The end effector comprises a body attached with an arm of the conditioning mechanism, an area on the body adapted to receive a conditioning member for conditioning a polishing member, and a bearing surface supporting that area on the body and providing a gimbal point about which the area rotates thereby minimizing digging of the conditioning member into the polishing member during polishing.
In still another aspect of the invention, a method of conditioning a polishing member in a chemical mechanical polishing apparatus for semiconductor wafers is provided. The method comprises providing a chemical mechanical polishing apparatus having a polishing region and a conditioning region, the conditioning region being opposite the polishing region, and cycling a polishing member around a plurality of rollers in a chemical mechanical polishing apparatus for semiconductor wafers such that, at any given time, a portion of the polishing member is in the polishing region and a portion of the polishing member is in the conditioning region. A conditioning member in a conditioning mechanism contacts the polishing member in the conditioning region and conditions the polishing member.
In yet another aspect of the invention, a combination of a chemical mechanical polishing apparatus and a conditioning mechanism is provided. The combination comprises a frame of the chemical mechanical polishing apparatus, a plurality of rollers mounted to the frame, a polishing member wrapped around the rollers such that such that, at any given time, a portion of the polishing member is in a polishing region and a portion of the polishing member is in a conditioning region opposite the polishing region. The conditioning is mechanism attached to the frame such that a conditioning member, when placed in the conditioning mechanism, can be moved to contact the polishing member in the conditioning region.